Pat the roast dry with paper towels, then generously season with salt and pepper. Sprinkle 2 tablespoons of flour all over the roast.
Heat a large skillet over medium-high heat with 2 tablespoons of olive oil. Sear the roast until nicely browned on all sides, about 5-7 minutes. Transfer the roast to the slow cooker.
Using the same skillet, add the onion, garlic, thyme, and rosemary and cook for 2 minutes. Slowly pour in the red wine and simmer until reduced by half, scraping the browned bits from the bottom of the skillet. Mix in the balsamic vinegar, worcestershire, and dijon mustard. Transfer to the slow cooker.
In a bowl, whisk the remaining 4 tablespoons of flour with 1 cup of broth (lumps are OK), then add to the slow cooker.
Add the remaining 1 cup of broth, carrots, and potatoes to the slow cooker. Season with ½ teaspoon salt and ¼ teaspoon black pepper.
Cook on low for 6-8 hours or until the venison roast is fork tender.
